“Turn on TV late in the evening and what are they trying to sell you?” asks Popular Science. “Coffee without caffeine … beverages to put lead in your eyelids … mattresses for spinal bliss. Poke around in a drugstore and what do you find? Sleeping pills, earplugs, black-velvet blindfolds … even lullaby records and how-to-sleep books. Obviously the strains of modern living have a lot of us worried about getting a good night’s sleep.”
Obviously. It’s a message you read about so often that the news articles start to blur together: People today are sleeping fewer hours than those happy slumberers of decades past, and you can blame your stress and your smartphone for it. But that passage above was printed in Popular Science in 1957, suggesting that for nearly 60 years Americans have been worried about the notion of a “modern” sleeplessness epidemic. And there is data to back this worry up: For instance, more than one-third of Americans don’t sleep enough, according to a U.S. Centers for Disease Control and Prevention report earlier this year — which is bad news, because studies have linked too little sleep with weight gain, diabetes, and heart disease, among other troubling consequences. Other headlines encourage the reader to contrast the sad state of sleep in America today with the snooze habits of the past — according to National Sleep Foundation data, 20 percent of people surveyed in 2009 said they slept fewer than six hours; compare that to the 12 percent who reported the same in the 1990s. “Centuries ago,” claims a CNN.com article on the NSF data, “people routinely slept eight to nine hours a day.”
Did they, though? Some fascinating and comprehensive new reviews of the scientific literature are questioning this idea. In 2012, for instance, a team of Australian researchers analyzed the results of 38 studies from around the globe, encompassing research conducted from the 1960s to the 2000s. That systematic review found that in most of these countries, the average amount of sleep citizens got per night increased in that time period. Meanwhile, this data set suggested that the number of people getting fewer than six hours of sleep per night had declined in many of the countries studied over the past four decades (though the authors say they found “inconsistent results” for the U.S. specifically). “This turns the current concept of an increasingly ‘sleep-deprived society’ on its head,” the authors write in Sleep Medicine Reviews, “and also challenges the notion that the penetration of personal technology into daily living, especially over the last 3 decades, has harmed our sleep patterns.”
It’s a conclusion that stands in direct contrast to those CDC and NSF studies, something that, as Quartz recently noted, may be explained by the subtle but distinct differences in the questions the researchers asked their study participants. Take the question as the CDC phrased it: “On average, how many hours of sleep do you get in a day?” As Quartz explains:
[A]nswers to such a question are likely to suffer from both conscious and unconscious biases, which may make people give a different answer than reality. Sleeping less, for instance, is associated with being more productive and some may consider it fashionable to say they sleep less. Some studies have also shown that people underestimate how much they actually sleep—especially those who suffer from insomnia.
Ask people how much sleep they tend to get, in other words, and their answers may not be as accurate as scientists would like them to be; this is a problem not just with the sleep literature, by the way, but with any kind of study that relies on self-reports. That 2012 systematic review, on the other hand, relied on time-use surveys — though these come with their own caveat, in that these respondents may be reporting the number of hours they spent in bed, which, as too many of us know from experience, may not be the same thing as time spent in blissful slumber.
To try and cut through some of this confusion, Shawn Youngstedt of Arizona State University and his colleagues recently analyzed 257 studies on “objective sleep duration” — that is, research conducted in the control-freak-friendly setting of a sleep laboratory. “As a sleep researcher, I hear this message over and over, and I was skeptical about it — that we’ve become a sleep-deprived society,” Youngstedt told Science of Us. Their results will appear in the August edition of the journal Sleep Medicine Reviews, under the title “Has adult sleep duration declined over the last 50+ years?” — and according to their data, the answer to that question appears to be no. In 1960, healthy adults slept, on average, about seven hours a night; the same was apparently true for the average healthy adult in 2013.
This is not to say that sleep deprivation isn’t a major health issue for many people, because, clearly, it is. For one, research has identified a racial disparity in the amount of sleep Americans get, in that black people tend to sleep worse than white people. And Youngstedt’s review of the literature isn’t perfect, either: Sleeping in a lab, accompanied by electrodes and weird machines monitoring your slumber, is likely not a very relaxing or natural-feeling experience. Sleep — perhaps especially quality of sleep — turns out to be a tricky thing to track. But to Youngstedt, the concern over our supposed sleep crisis today might actually be the result of improvements in the scientific study of sleep — a field that has really only been around since the 1970s, he said. “I think part of it is we’re intimately more aware about sleep than we were 30, 40, 50 years ago,” Youngstedt said. “And so there’s a lot more concern about [it]. The same percentage of the population are shift workers now as 40, 50 years ago — it’s just that now we know that shift work is extremely hazardous. And apnea, too — no one had any idea what apnea was 40, 50 years ago.“
Also of note: Seven, not eight, turns out to be the number many sleep scientists are now arguing is the “optimal” number of hours to sleep, and some recent research is showing that too much sleep — especially nine hours or more — is not great for your health, either. Interestingly, seven is also about the amount of time that hunter-gatherer groups in Bolivia, Tanzania, and South Africa slept each night on average, according to one study published last fall. These are people, in other words, who do not have smartphones and Netflix to keep them awake all night, and yet they tend to get about as much sleep as people in Western nations. As neuroscientist Jerome Siegal, who led the study, told Science magazine, “Before we tell people they need more sleep, we need to make sure this is true.”